Radio shielded spark plug



Dec. 19, 1939. o. c. ROHDE RADIO SHIELDED SPARK PLUG amznkw Filed Sept.23, 1938 d MW ea Patented Dec. 1 9, 193@ UNITED STATES PATENT FFlCERADIO- SHIELDED SPARK PLUG Application September 23, 1938, Serial No.231,410

2 Claims.

This invention relates to radio shielded spark plugs, and isparticularly directed to improved features of construction of such sparkplugs. v

The primary object of the invention is the provision of a radio shieldedspark plug which is easily assembled in a manner to provide againstleakage and in which the parts subject to wear are amply protected.

Another object of the invention is the provision of a radio shieldedspark plug in which the center electrode is held in place by acompactible insulating material having a high heat conductivity so thata gas-tight seal is provided around the center electrode and at the sametime heat from the electrode is dissipated to the atmosphere. I

Other objects and advantages of the invention will become apparent asthe description proceeds, reference being had to the accompanyingdrawing, in which- Figure 1 is a longitudinal section of a radioshielded spark plug embodying the features of the present invention, andFig. 2 is a section on line 2-2 of Fig. 1.

Referring to the drawing, I designates a shell having the usual externalthreads for engagement in a cylinder head of an internal combus tionengine, and carrying an outer electrode 2 at its lower end. Anelongated,tubular metallic jacket 3 is received in threaded engagementwith the upper end of the shell I and the joint between the two partsissealed by a gasket 5 compressed between the lower end of the jacketand a cooperating shoulder 6 formed on the interior of the shell I. Itwillbe seen that the shell and the tubular jacket are functionallyintegral after being assembled.

A center electrode 8 is held within the jacket 3 and extends below thismember into cooperative relationship with the outer electrode 2. A micasleeve l0 surrounds the center electrode-for a portion of its length,and, adjacent the lower end of the electrode, is in turn surrounded by astack of graduated mica washers I! or other suitable insulating body. Itis, of course, necessary that the spark plug be sealed against leakagearound interlock with each other to maintain the positions to which theyare forced by the high tamping pressure. Thus, if the powder is tampedin place under a high pressure, the mica sleeve Ill is forced againstthe center electrode and, since 6 the powder maintains its tampedposition by interlocking of its particles, the sleeve is held tightly inplace. For a portion of the length of the center electrode, as at 3 thetamped powder is in direct contact with the metal. The powder 10 usedmay consist principally of talc and a borate of an alkaline earth metalas described and claimed in the copending application Serial No.138,397. Although the borate may be omitted where other insulation isarranged so that cur- 15 rent can pass through the powder only by a longpath. This powder, when compacted, has a heat conductivity comparable tothat of cold rolled.- steel, so that heat drawn from the combustion.

chamber of the engine through the center elecg0 trode flows very rapidlythrough the compacted insulating material to the jacket 3 where it isdissipated to the atmosphere. v

A contact plate It is placed over the mass of powdered insulatingmaterial and is maintained 25 in electrical contact with, the centerelectrode in any suitable manner as by upsetting the end of theelectrode over the plate.

The upper portion of the jacket 3, above the center electrode, is linedwith any suitable insu- 30 lating body such as a mica sleeve l8. Thissleeve must extend below washer l4, and should extend below the top ofsleeve ID if powder I3 is not borated. Mica or other mechanicallyrelatively insubstantial insulating material used in this con- 35nection must be protected against fraying and abrasion at the exposedupper end by repeated insertions of the ignition lead assembly, whichlatter is designated 20. The ignition wire 2| carries a suitable contactat its inner end, which 4 includes a spring 22 designed to bear againstcontact plate I4 when the parts are in assembled position. The ignitionlead assembly forms no part of the present invention, and is shownentirely by way of illustration. Since the ignition lead 45 or conductoris housed within a metal chamber and hence subjected to unusually hightemperatures some-means must be found to protect the end of theconductor against heat flowing from the combustion chamber throughthecenter electrode. By using the compacted powder having a very high heatconductivity this heat is dissipated before it reaches the point ofconnection between the conductor and center electrode. In

this way, the possibility of burning the tip of the conductor 2| ispractically obviated.

To protect the sleeve l8, the present invention provides an extremelysimple and expedient means in the form of a snap ring 24 which isreceived in a suitable annular recess in the upper end of the jacket 3.The snap ring has an internal diameter smaller than the inner diameterof the sleeve IB. The ring 24 is held against any outward displacementby rolling the extreme end of the jacket inwardly as at 26 to overliethe ring, or by otherwise pounding a groove in the inner surface ofjacket 3. It will be seen that the sleeve 18 terminates slightly shortof the snap ring 24 so that any force exerted on the latter will not becommunicated to the relatively insubstantial insulating material, butwill be transmitted directly to and absorbed by the jacket 3.

Screw threads 28 are formed on the upper end of the jacket forengagement with the coupling 29 of the ignition lead assembly 20.Obviously, any suitable type of harness for the ignition wire may beused.

While the invention has been disclosed in connection with a spark plughaving a particular form and disposition of the parts, it will bereadily appreciated that numerous changes will suggest themselves tothose skilled in the art. It should be expressly understood that suchchanges may be made without departing from the spirit of the inventionas defined in the appended claims.

The invention claimed is:

1. In a radio shielded spark plug having a metallic shell and a. jacketfunctionally integral with said shell, a center electrode, a mica sleevesurrounding said center electrode for a portion of its length, and meansto fix said center electrode in said jacket comprising a body ofcompacted powder surrounding said sleeve and electrode, said powderbeing of a nature such that the particles interlock when subjected topressure and remain interlocked when the pressure is released, wherebysaid mica sleeve is held in tight engagement with said center electrode.

2. In a radio shielded spark plug having a metallic shell and a tubularmetallic jacket functionally integral with said shell adapted to receivean ignition lead and contact, a center electrode, and a body ofcompacted powder occupying at least the major portion of the spacebetween said electrode and jacket, said powder being of a nature suchthat the particles interlock when subjected to pressure and remaininterlocked when the pressure is released and the powder having a heatconductivity in the order of that of cold rolled steel whereby heat fromthe center electrode is dissipated through said metallic jacket.

EDITH E. ROHDE. Executria: of the Estate of Otto C. Rohde,

Deceased.

